1. Field of the Invention
The present invention relates to a method for manufacturing barium-strontium titanate fine powder which is known as one of dielectric materials.
2. Description of the Prior Art
Recently, a method for forming ceramic material, which is a functional electronic material, into fine powder has been studied from various angles. As one of the applications of such fine powder of the ceramic material, there is such application that the fine powder is used to produce a capacitor. As electronic products are made small in size and high in density, the capacitor is also requested to be made small in size, light in weight, large in capacitance and improved in high frequency characteristic similarly to other electronic parts. For this reason, in a ceramic capacitor, in order to make its thickness thin and uniform, the ceramic material must be formed into fine powder.
As one of such ceramic materials, there is known barium-strontium titanate Ba.sub.1-x Sr.sub.x TiO.sub.3 (0&lt;x&lt;1). As a prior art method for manufacturing such fine powder, there is a solid phase reaction method which uses BaCO.sub.3, SrCO.sub.3 and TiO.sub.2 as the raw material. In this solid phase reaction method, BaCO.sub.3, SrCO.sub.3 and TiO.sub.2 are weighted so as to make a desired composition, ground in a ball mill and then mixed to one another. Thereafter, the product is subjected to pressmolding, calcined at high temperature of 1300.degree. to 1500.degree. C., ground in the ball mill and the like and then subjected to to the sieving or screening treatment, thus fine powder being obtained. However, according to this solid phase reaction method, it takes a long time to grind the materials in the ball mill and in addition impurity and powder of large size are inevitably mixed to the product. Further, there is a defect that a particle size distribution grows worse and so on. As other synthesizing method, there is an oxalate method. In this method, complex metal oxalate is synthesized and then roasted to thereby make fine powder of Ba.sub.1-x Sr.sub.x TiO.sub.3. According to this method, a process for synthesizing uniform complex metal oxalate is complicated and in addition, organic compound is used so that the manufacturing cost becomes high. Further, although the desired fine powder is obtained, the powder is essentially succeeding the original oxalate powder. To avoid the formation of the powder having the original oxalate structure a problem of the sintering between the powders occurs so that this method does not yet reach the industrial production stage at present. Furthermore, a method in which metal alkoxide is used to produce complex metal titanate fine powder of barium-strontium titanate Ba.sub.1-x Sr.sub. x TiO.sub.3 has recently been studied and developed. This method must use special organic compound such as metal alkoxide so that the manufacturing cost thereof becomes considerably high as compared with the oxalate method.